The seven blasts that went off on seven different trains of Mumbai's Western Railway suburban network crippled the busiest railway artery in the world.

Mumbai has a population of about 18 million. And more than 6.5 million of them travel daily on the city's three suburban train systems -- the Western Railway, the Central Railway and the Harbour line.

The Western Railway suburban network -- that operates through 60 kilometres servicing 28 stations between Churchgate in south Mumbai and Virar in north Mumbai -- is the busiest corridor, in terms of passengers using it, of the three rail networks. The next busiest corridor in the world is the Central Railway.